This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The purpose of this trial is to assess the prevalence of the BK, CMV, and adenovirus in pediatric patients undergoing hematopoietic stem cell transplantation. We will perform longitude analysis of the presence and levels of BK, CMV, and adenovirus in the urine and blood of pediatric patients undergoing hematopoietic stem cell transplant (HSCT). We expect to correlate levels of BK, CMV, and adenovirus with the following: 1) underlying disease (malignant vs. genetic), 2) prior medications, 3) transplant type (sibling, unrelated donor, cord blood, haploidentical), 4) hemmorhagic cystitis or other possible BK, CMV, or adenovirus virus-related disease, 5) inter-current anti-viral therapy, 6) immune function recovery, and 7) immune suppression intensity.